1. Field of the Invention
The present invention relates to a plasma processing apparatus and, more specifically, to a plasma processing apparatus suitable for forming a metal film, such as a TiN film, for an electronic device, such as a semiconductor device.
2. Description of the related Art
Electronic devices, such as semiconductor devices, have progressively been miniaturized. The size of contact holes has progressively been reduced with the miniaturization of semiconductor integrated circuits and the conventional thin film forming techniques, for example, the bias sputtering process for forming aluminum thin films, have become unable to cope with the progressive miniaturization of semiconductor integrated circuits. Accordingly, the blanket tungsten chemical vapor deposition process (hereinafter referred to as "blanket tungsten CVD process"), which is capable of forming films that have a high coverage, has become attractive in recent years.
Referring to FIG. 4, the blanket tungsten CVD process forms a layer insulating layer 104 over the surface of a silicon wafer 100 provided with a diffused layer 102, forms an opening 106 through the layer insulating layer 104, forms a contact layer 108 of TiN or TiON over the surface of the layer insulating layer 104 and in the opening 106, forms a tungsten layer 110 over the contact layer, and then removes the tungsten layer 110 by etching, leaving only a portion of the tungsten layer 110 formed in the opening 106 to complete a contact hole. Since the adhesion of the tungsten layer 110 to the silicon wafer 100 is not very high, it is essential to form the contact layer 108 of TiN or the like between the silicon wafer 100 and the tungsten layer 110. If the contact layer 108 is unable to cover the inner surface of the opening 106 satisfactorily, it is possible that a void 112 is formed in a portion of the tungsten layer 110 deposited by a CVD process in the opening 106 formed in the layer insulating layer 104.
Since TiCl.sub.4 is used as a source material for forming the contact layer 108 of TiN by a CVD process, the contact layer 108 is liable to contain Cl. Refer to, for example, "Photo Assisted LP-CVD TiN for Deep Submicron Contact Using Organotitanium Compound", Koichi Ikeda. et al., 1990 Symposium on VLSI Technology, pp. 61-62 for the further details. To avoid such a problem, an electron cyclotron resonance plasma CVD process (hereinafter referred to as "ECR plasma CVD process") for forming a TiN film is proposed in Akabori et al., "Ouyou Butsuri Gakkai Yokou-shu, Spring, 1990" 29a-ZA-6, p. 591. It is reported in this paper that the ECR plasma CVD process was able to form a TiN film in a high coverage and the Cl content of the TiN film was reduced when the TiN film was formed at a temperature on the order of 650.degree. C.
It is known that the mode of growth of TiN crystals is dependent on temperature, that is, a coarse TiN film is formed when TiN crystals grow at a relatively low temperature and, in an extreme case, TiN particles are formed Refer to Kagaku Kogakkai, "CVD Handbook", pp. 578, 583, Asakura Shoten K.K., Jun. 20, 1991.
When forming a TiN film on a wafer by a blanket tungsten CVD process, the wafer is placed in a film forming chamber and is heated at a temperature on the order of 650.degree. C. Although a TiN film of good quality is formed over the surface of the wafer, a coarse TiN film is formed over the inner surface of the walls of the film forming chamber and, in an extreme case, TiN particles are formed because the walls of the film forming chamber are not heated, which reduces the yield of the semiconductor device manufacturing process. Accordingly, the development of an ECR plasma CVD apparatus capable of forming TiN film or the like without producing particles has been desired.